Conventionally, there has been known a technology regarding a power transmission apparatus in which an engine is automatically stopped or started in predetermined cases. For example, see the description disclosed by patent document 1.
The power transmission apparatus disclosed by patent document 1 includes an engine which serves as a power source, a hydraulic pump to discharge hydraulic oil, a clutch interposed between an output shaft of the engine and an input shaft of the hydraulic pump, an electric motor (electric motor) connected to the input shaft of the hydraulic pump, a flywheel fixedly disposed on the input shaft of the electric motor, an actuator to be driven based on the hydraulic oil supplied from the hydraulic pump, and an operating means configured to operate the actuator.
When load applied to the actuator is close to zero, the clutch is disconnected, and the engine is stopped, and the hydraulic pump is driven by the electric motor. Also, when the operating means is operated by an operator in a state where the engine is stopped (that is, when it is predicted that the load is applied to the actuator), the clutch is connected, and the engine is restarted by the inertia of the flywheel or the driving force of the electric motor.
Thus, when the load is not applied to the actuator, that is, when an operation is not carried out, the engine is stopped, thereby preventing wasteful fuel consumption, and when the operation is restarted by the actuator, the engine can swiftly be started.
However, regarding the power transmission apparatus disclosed by patent document 1, the electric motor to drive the hydraulic pump is used as a starter motor to start the engine. Accordingly, when the engine is restarted, there is a case where the number of revolutions of the electric motor is reduced. In this case, the number of revolutions of the hydraulic pump is reduced along with the reduction of the number of revolutions of the electric motor, which reduces the flow rate of the hydraulic oil supplied to the actuator. Accordingly, there is a disadvantage in that the operating speed of the actuator is reduced, and the operation feeling of the actuator used by the operator deteriorates.